title: Different endosomal proteolysis requirements for antigen processing of two T-cell epitopes of the M5 protein from viable Streptococcus pyogenes.
abstract: We studied endosomal proteolysis of the surface fibrillar M5 protein from viable Streptococcus pyogenes as an essential step involved in major histocompatibility complex class II-restricted antigen processing of two immunodominant CD4(+) T-cell epitopes (17-31/Ed and 308-319/Ad). Intracellular proteolysis of viable streptococci for presentation of 17-31, bound by serine proteinase cleavage sites, was mediated by serine proteinases, whereas processing of soluble recombinant M5 protein required in addition cysteine proteinases. Furthermore, processing of 17-31 was resistant to ammonium chloride and thus was not dependent on endosome acidification. Cysteine and serine proteinase cleavage sites were located adjacent to 308-319, and its processing was dependent on serine, cysteine, and aspartic proteinases, as well as on endosomal acidification. The data suggest that antigen processing of two major T-cell epitopes on streptococcal M5 protein occurred in different endosomal compartments by different classes of intracellular proteinases.
authors.affiliation: Department of Immunology, School of Microbiological, Virological, and Immunological Sciences, The Medical School, University of Newcastle upon Tyne, Framlington Place, Newcastle upon Tyne, Tyne and Wear, NE2 4HH, United Kingdom.
authors.forename: A A
authors.initials: AA
authors.lastname: Delvig
authors.forename: J H
authors.initials: JH
authors.lastname: Robinson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000942:Antigens, Bacterial / Q000276:immunology / Q000378:metabolism*; D001426:Bacterial Proteins / Q000276:immunology / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism*; D000939:Epitopes / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D051379:Mice; D008969:Molecular Sequence Data; D013297:Streptococcus pyogenes / Q000378:metabolism*; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism*
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D000939:Epitopes; D003546:Cysteine Endopeptidases